Andrei Alexandrescu (See Website For Email) wrote:
> janderson wrote:
>> Andrei Alexandrescu (See Website for Email) wrote:
>>> My previous post defines max by availing itself of a metafunction called
>>> varargs_reduce. Your challenge is to define it. varargs_reduce takes an
>>> alias which it assumes is a function of two arguments, and it defines a
>>> vararg function that applies that alias repeatedly, similarly to the
>>> reduce primitive that is present in functional languages. Again, for
>>> background on functional reduce, see e.g.:
>>>>>> http://www.joelonsoftware.com/items/2006/08/01.html>>>>>> Define varargs_reduce to deduce the result type properly, and to generate code as efficient as possible.
>>>>>>>>> Andrei
>>>>>> While your at it. What about a multi-threaded version? ie Each function that is called is placed on one of 4 threads.
> > That's a good point, and goes right to the core of my solution, which (similarly to Bruno Medeiros') arranges operations in an optimal way for superscalar evaluation, e.g. max(a, b, c, d) is expanded not to:
> > max2(max2(max2(a, b), c), d)
> > but instead to:
> > max2(max2(a, b), max2(c, d))
Assumes the operation is associative. That may not always be the case; it's not even necessarily true that the function takes arguments of identical types.
Silly example:
char[] accumulate(char[] arr, char element) { return arr ~= element; }
Of course, you could *require* that the operation is associative, but I didn't see that anywhere in the specification.
And as far as I can tell, that generally isn't assumed for reduce.
For instance in Lisp, REDUCE is either left-to-right or right-to-left (depending on a flag)[1].
In Python, it's always left-to-right[2].
(those were the ones I could most easily find with a quick Google search)
[1]: http://www.lisp.org/HyperSpec/Body/fun_reduce.html
[2]: http://docs.python.org/lib/built-in-funcs.html

Kevin Bealer wrote:
> == Quote from Andrei Alexandrescu (See Website for Email)
> (SeeWebsiteForEmail@erdani.org)'s article
>> My previous post defines max by availing itself of a metafunction called
>> varargs_reduce. Your challenge is to define it. varargs_reduce takes an
>> alias which it assumes is a function of two arguments, and it defines a
>> vararg function that applies that alias repeatedly, similarly to the
>> reduce primitive that is present in functional languages. Again, for
>> background on functional reduce, see e.g.:
>>>> http://www.joelonsoftware.com/items/2006/08/01.html>>>> Define varargs_reduce to deduce the result type properly, and to
>> generate code as efficient as possible.
>>>> Andrei
> > There is a really simple solution, but I'm not sure if it does the right thing
> with respect to your wording above. What exactly is meant by deducing the result
> type properly? Specifically, if the input types are different kinds of objects,
> is the result expected to have the same type as a linear sequence of operations?
> > 1. Can we assume the type conversions are non-cyclic?
> 2. Should we assume that the delegate looks like: T dg(T, T), or like: T dg(U, V)
> 3. If the signature is T dg(U, V), can we assume that type conversions are non-cyclic?
> > Cyclic types: (requires more template logic than actually shown here)
> > Rock add(Paper x, Scissors y);
> Paper add(Scissors x, Rock x);
> Scissors add(Rock x, Paper y);
> > If this kind of stuff is permitted, the solution is possible but a lot messier.
Interesting point. I think varargs_reduce can safely assume that linear reduction always works f(f(f(f(...f(a1, a2), a3), a4), ...). My solution optimizes more aggressively by assuming that reduction can be performed in any order.
Your solution is less optimal because it uses a delegate. Ideally you just use an alias and deduce the result type by simply using the alias.
Andrei

Frits van Bommel wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> janderson wrote:
>>> Andrei Alexandrescu (See Website for Email) wrote:
>>>> My previous post defines max by availing itself of a metafunction called
>>>> varargs_reduce. Your challenge is to define it. varargs_reduce takes an
>>>> alias which it assumes is a function of two arguments, and it defines a
>>>> vararg function that applies that alias repeatedly, similarly to the
>>>> reduce primitive that is present in functional languages. Again, for
>>>> background on functional reduce, see e.g.:
>>>>>>>> http://www.joelonsoftware.com/items/2006/08/01.html>>>>>>>> Define varargs_reduce to deduce the result type properly, and to generate code as efficient as possible.
>>>>>>>>>>>> Andrei
>>>>>>>>> While your at it. What about a multi-threaded version? ie Each function that is called is placed on one of 4 threads.
>>>> That's a good point, and goes right to the core of my solution, which (similarly to Bruno Medeiros') arranges operations in an optimal way for superscalar evaluation, e.g. max(a, b, c, d) is expanded not to:
>>>> max2(max2(max2(a, b), c), d)
>>>> but instead to:
>>>> max2(max2(a, b), max2(c, d))
> > Assumes the operation is associative. That may not always be the case; it's not even necessarily true that the function takes arguments of identical types.
> > Silly example:
> char[] accumulate(char[] arr, char element) { return arr ~= element; }
I think this ia a good point. Probably varargs_reduce must be linear to make the most conservative assumptions. There is always the chance of defining varargs_reduce_parallel. Thanks!
Andrei

Andrei Alexandrescu (See Website For Email) wrote:
> Frits van Bommel wrote:
>> Andrei Alexandrescu (See Website For Email) wrote:
>>> janderson wrote:
>>>> Andrei Alexandrescu (See Website for Email) wrote:
>>>>> My previous post defines max by availing itself of a metafunction called
>>>>> varargs_reduce. Your challenge is to define it. varargs_reduce takes an
>>>>> alias which it assumes is a function of two arguments, and it defines a
>>>>> vararg function that applies that alias repeatedly, similarly to the
>>>>> reduce primitive that is present in functional languages. Again, for
>>>>> background on functional reduce, see e.g.:
>>>>>>>>>> http://www.joelonsoftware.com/items/2006/08/01.html>>>>>>>>>> Define varargs_reduce to deduce the result type properly, and to generate code as efficient as possible.
>>>>>>>>>>>>>>> Andrei
>>>>>>>>>>>> While your at it. What about a multi-threaded version? ie Each function that is called is placed on one of 4 threads.
>>>>>> That's a good point, and goes right to the core of my solution, which (similarly to Bruno Medeiros') arranges operations in an optimal way for superscalar evaluation, e.g. max(a, b, c, d) is expanded not to:
>>>>>> max2(max2(max2(a, b), c), d)
>>>>>> but instead to:
>>>>>> max2(max2(a, b), max2(c, d))
>>>> Assumes the operation is associative. That may not always be the case; it's not even necessarily true that the function takes arguments of identical types.
>>>> Silly example:
>> char[] accumulate(char[] arr, char element) { return arr ~= element; }
> > I think this ia a good point. Probably varargs_reduce must be linear to make the most conservative assumptions. There is always the chance of defining varargs_reduce_parallel. Thanks!
> > > Andrei
I think that would be best (having a semi-seperate _parellel version). I also wonder about applying this same "feature" to functions of 3 or 4 arguments (or even arbitrary! so long as none are themselves variadic), but that could come later.
-- Chris Nicholson-Sauls

"Andrei Alexandrescu (See Website for Email)" <SeeWebsiteForEmail@erdani.org> wrote in message news:ep4i7p$2n1t$4@digitaldaemon.com...> My previous post defines max by availing itself of a metafunction called varargs_reduce. Your challenge is to define it. varargs_reduce takes an alias which it assumes is a function of two arguments, and it defines a vararg function that applies that alias repeatedly, similarly to the reduce primitive that is present in functional languages. Again, for background on functional reduce, see e.g.:
>> http://www.joelonsoftware.com/items/2006/08/01.html>> Define varargs_reduce to deduce the result type properly, and to generate code as efficient as possible.
>>> Andrei
This post is not meant to be inflammatory.
Answer me this: are you just toying with us, tempting us with things which are unimplementable without new features which are secretly being developed for D? Or are you just surreptitiously trying to get the community to write a bunch of standard library metacode for you? ;)
How about this: start a thread in which you disclose all the fancy features you (you plural, you and Walter, since you now seem to be the _team_ designing D) have been planning.
For that matter, is coming up with crazy new features like inout returns and opImplicitCast _all_ Walter's doing? Or is he fixing bugs?

Jarrett Billingsley wrote:
> "Andrei Alexandrescu (See Website for Email)" <SeeWebsiteForEmail@erdani.org> wrote in message news:ep4i7p$2n1t$4@digitaldaemon.com...>> My previous post defines max by availing itself of a metafunction called
>> varargs_reduce. Your challenge is to define it. varargs_reduce takes an
>> alias which it assumes is a function of two arguments, and it defines a
>> vararg function that applies that alias repeatedly, similarly to the
>> reduce primitive that is present in functional languages. Again, for
>> background on functional reduce, see e.g.:
>>>> http://www.joelonsoftware.com/items/2006/08/01.html>>>> Define varargs_reduce to deduce the result type properly, and to generate code as efficient as possible.
>>>>>> Andrei
> > This post is not meant to be inflammatory.
Definitely not taken as such.
> Answer me this: are you just toying with us, tempting us with things which are unimplementable without new features which are secretly being developed for D? Or are you just surreptitiously trying to get the community to write a bunch of standard library metacode for you? ;)
It's really easy. I can't right now disclose all of my agenda for objective reasons (I will do it later), but the gist of the matter is simple:
1. There are some simple tests for a language gaging very precisely the power of that language
2. I want D to pass those tests
3. I want to increase community's awareness of the importance of those tests for larger use cases, as well as gather ideas from the community about how to overcome D's shortcomings in passing the tests.
> How about this: start a thread in which you disclose all the fancy features you (you plural, you and Walter, since you now seem to be the _team_ designing D) have been planning.
We are doing it already, e.g. by describing my suggested max implementation. But I don't want to do that preemptively, because I'd bias future responses. I wished, for example, that somebody could suggest a better design instead of "storageof(T) T".
> For that matter, is coming up with crazy new features like inout returns and opImplicitCast _all_ Walter's doing? Or is he fixing bugs?
Walter and I have been discussing these issues and we have agreement on the necessity of certain features (of which indeed better inout handling and opImplicitCast are two). At this point, we don't have much more of a design than what I've already shown. For all I know, Walter hasn't started implementing any of them.
Andrei

Andrei Alexandrescu (See Website For Email) wrote:
[snip]
> It's really easy. I can't right now disclose all of my agenda for objective reasons (I will do it later), but the gist of the matter is simple:
> > 1. There are some simple tests for a language gaging very precisely the power of that language
> > 2. I want D to pass those tests
> > 3. I want to increase community's awareness of the importance of those tests for larger use cases, as well as gather ideas from the community about how to overcome D's shortcomings in passing the tests.
That's great, Andrei. And I, for one, truly want to see some of those changes happen (such as read-only arrays, covered by the const you talk of).
However, there are also some rather pressing matters of fixing stuff that is simply broken, and is hampering attempts to build real, live, useful apps at this time. Yeah, new features are sexy cool, and fixing long-standing issues ain't.
How about taking a long hard look at what sucks in D right now, and making those a primary priority? Having read many of your posts since yesterday, it seems you've identified a number of those. Great! Yet, you guys are apparently pressing ahead with wonderful new stuff instead? Like, for instance, an updated GC? When did that ever top the list of real-world issues for D?
To anticipate a question:
There's some serious issues with templates in libs (you really can't put them there successfully), some serious issues with debuggers not being able to locate source-files for templates; lots of problems related to real-world, end-user, /usability/ of the language on a daily basis.
I submit that such issues are just as important a test to pass than the ones you allude to. Dare I say, perhaps more so for people actually using the language right now?
Regards;
- Kris

kris wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
> [snip]
> >> It's really easy. I can't right now disclose all of my agenda for objective reasons (I will do it later), but the gist of the matter is simple:
>>>> 1. There are some simple tests for a language gaging very precisely the power of that language
>>>> 2. I want D to pass those tests
>>>> 3. I want to increase community's awareness of the importance of those tests for larger use cases, as well as gather ideas from the community about how to overcome D's shortcomings in passing the tests.
> > That's great, Andrei. And I, for one, truly want to see some of those changes happen (such as read-only arrays, covered by the const you talk of).
> > However, there are also some rather pressing matters of fixing stuff that is simply broken, and is hampering attempts to build real, live, useful apps at this time. Yeah, new features are sexy cool, and fixing long-standing issues ain't.
> > How about taking a long hard look at what sucks in D right now, and making those a primary priority? Having read many of your posts since yesterday, it seems you've identified a number of those. Great! Yet, you guys are apparently pressing ahead with wonderful new stuff instead? Like, for instance, an updated GC? When did that ever top the list of real-world issues for D?
I'm afraid I am not in the position to help here. All I'm really doin' is bitchin'. Walter does the actual work, and prioritizing and implementing is entirely his charter.
That being said, my view on what should be fixed in D is a bit different. For example, as I said, one of my main foci is putting a lead sarcophagus around "inout" before its radioactive waste affects too much code that will become broken later. Also, implicit conversion rules will change, and again I want to get that in ASAP so not too much code suffers. And so on.
> To anticipate a question:
> > There's some serious issues with templates in libs (you really can't put them there successfully), some serious issues with debuggers not being able to locate source-files for templates; lots of problems related to real-world, end-user, /usability/ of the language on a daily basis.
> > I submit that such issues are just as important a test to pass than the ones you allude to. Dare I say, perhaps more so for people actually using the language right now?
I entirely agree. Figuring out priorities is Walter's call. Let's keep our fingers crossed :o).
Andrei

Andrei Alexandrescu (See Website For Email) wrote:
> kris wrote:
> >> Andrei Alexandrescu (See Website For Email) wrote:
>> [snip]
>>>>> It's really easy. I can't right now disclose all of my agenda for objective reasons (I will do it later), but the gist of the matter is simple:
>>>>>> 1. There are some simple tests for a language gaging very precisely the power of that language
>>>>>> 2. I want D to pass those tests
>>>>>> 3. I want to increase community's awareness of the importance of those tests for larger use cases, as well as gather ideas from the community about how to overcome D's shortcomings in passing the tests.
>>>>>> That's great, Andrei. And I, for one, truly want to see some of those changes happen (such as read-only arrays, covered by the const you talk of).
>>>> However, there are also some rather pressing matters of fixing stuff that is simply broken, and is hampering attempts to build real, live, useful apps at this time. Yeah, new features are sexy cool, and fixing long-standing issues ain't.
>>>> How about taking a long hard look at what sucks in D right now, and making those a primary priority? Having read many of your posts since yesterday, it seems you've identified a number of those. Great! Yet, you guys are apparently pressing ahead with wonderful new stuff instead? Like, for instance, an updated GC? When did that ever top the list of real-world issues for D?
> > > I'm afraid I am not in the position to help here. All I'm really doin' is bitchin'.
Drat ... that's apparently all I'm achieving too :(
> Walter does the actual work, and prioritizing and implementing is entirely his charter.
> > That being said, my view on what should be fixed in D is a bit different. For example, as I said, one of my main foci is putting a lead sarcophagus around "inout" before its radioactive waste affects too much code that will become broken later. Also, implicit conversion rules will change, and again I want to get that in ASAP so not too much code suffers. And so on.
Aye, and that is certainly appreciated. Some of the items you've mentioned recently have long been festering sores for many. It'll certainly be refreshing to see some attention focused upon those.
Regarding implicit conversion rules -- are you including the "issues" currently surrounding signature-matching when using constants?
> >> To anticipate a question:
>>>> There's some serious issues with templates in libs (you really can't put them there successfully), some serious issues with debuggers not being able to locate source-files for templates; lots of problems related to real-world, end-user, /usability/ of the language on a daily basis.
>>>> I submit that such issues are just as important a test to pass than the ones you allude to. Dare I say, perhaps more so for people actually using the language right now?
> > > I entirely agree. Figuring out priorities is Walter's call. Let's keep our fingers crossed :o).
Hehe; superstition :-p
Well, thanks for replying. The clarification is much appreciated, though I'm honestly sad to hear you're not more deeply involved.
Cheers;
- Kris